In the extraction of viscous hydrocarbon products such as crude oil from a subterranean reservoir or formation, production is often hampered by a number of factors. These inlcude the inability of the gas pressure in the formation to urge the viscous product to the surface. Similarly, in the production of bitumen from a tar sand substrate the viscosity of the bitumen is such that it is virtually immovable while retained in its in situ state.
Toward facilitating the production of these viscous hydrocarbon products, methods have been provided to lessen the viscosity of the retained products and to promote their movement through the substrate and toward a producing well.
In the instance of bitumen contained within tar sand formations, the latter can be relatively thin in comparision to the normal subterranean reservoir wherein crude oil is retained. A productive layer, however, even though comprised of tar sands, can be hundreds of feet in thickness. It has therefore become practical when extracting bitumen or crude oil from such a layer, to utilize horizontal rather than vertical or diverter type wells.
In such an installation, the well or wells are spudded into the substrate in such manner as to approach the overburden layer either vertically or at an angle. Thereafter, as the wellbore enters and penetrates the productive layer, it is diverted into a substantially horizontal direction. Preferably, the wellbore will be urged in a direction such that it will run concurrently with the productive layer.
With the or more horizontal wells formed into a productive layer, it is possible to use at least one of the wells for injecting a hot stimulating fluid. The latter usually comprises water or steam which are forced into the formation. In either instance, contact between the hot stimulating medium and the hydrocarbon will gradually transform the latter into flowable condition.
Steam, with or without additive materials, is often utilized as the stimulating medium. Thereafter, the resulting hot condensate will form an emulsion with the flowable hydrocarbon and be in producible form.
As a general practice, thermal stimulation of a productive layer is initiated by first raising the environment of the well or wells to a temperature at which the viscosity of the contained hydrocarbon is reduced. Thereafter, further injection of pressurized steam will urge the flowable hydrocarbon emulsion toward a lower pressure producing well or toward a lower pressure portion of the single well.
If a single well is used, the huff and puff method for producing can be employed by alternately injecting hot stimulating fluid selectively into the well. Thereafter, a pumping procedure extracts the emulsion from the well for further treatment and separation.
In the instance of a productive substrate which covers a great depth, a considerable amount of steam can be used before the hydrocarbon is produced. In other words, when steam is injected into an expansive productive layer that runs for a considerable depth, much of the steam will be dissipated and wasted. Further, in such an instance, there is presently lacking a feasible way of accurately determining the extent to which the production layer is being heated and produced.
As in any operation where hydrocarbon is produced from a subterranean formation, it is a primary objective to remove the greatest amount of product while using a minimal amount of stimulating medium. It is thus mandatory, in order to achieve a higher degree of efficiency, that the bitumen or the hydrocarbon containing layer be swept or penetrated in a manner that the maximum amount of hydrocarbon is removed with as little wasted heat as possible.
This objective is achieved as hereinafter described, by the particular disposition of wells within a productive layer whereby to regulate the flow and function of a stimulating medium which is injected into the formation.
There is presently disclosed a method for producing a viscous hydrocarbon such as bitumen or crude oil from a subterranean layer or formation by a plurality of wells or peferably from a well array. The latter is formed in said layer in a manner such that the respective wells lie in a substantially horizontal alignment, vertically spaced, and positioned at different levels or depths.
The respective wells preferably originate from a common area or pad at the surface. They thereafter penetrate the overburden, and are diverted into a substantially horizontal direction through the productive layer. Production of hydrocarbon emulsion thereafter results by virtue of the selective introduction of a hot pressurized stimulating fluid in a manner that the productive layer will be most effectively swept and drained of the contained hydrocarbon.
To most effectively sweep a formation, and optimize the usage of steam, a plurality of horizontal wells are formed as noted, in substantially vertical alignment. The wells are spaced to define a series of contiguous, horizontal formation segments therebetween. The latter in effect are striated by the respective parallel wells.
Thereafter, selective introduction of a heating medium into the various wells progressively heats the contiguous segments and results in an orderly, efficient downward flow of the hydrocarbon in emulsion form. As each parallel segment is heated and produced, the next lower adjacent segment is similarly treated and produced.
It is therefore an object of the invention to provide an efficient method to thermally stimulate a subterranean formation for the production of viscous hydrocarbons therefrom.
A further object is to provide a method for the stimulation of a viscous hydrocarbon containing substrate in a manner to cause an orderly downward flow of hydrocarbon emulsion into a producing well.
Another object is to provide an array of horizontally disposed, and vertically spaced apart wells within a subterranean productive layer, which arrangement will assure the most efficient extraction of hydrocarbon product in response to the introduction of a hot stimulating fluid into the substrate.
A still further object is to provide a method and an arrangement of wells in a tar sand formation for producing bitumen emulsion sequentially from adjacent horizontal segments of the productive layer.